Modern

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Modern Eco-friendly Pulping Bleaching
Techniques

• By
• Dr. Vimlesh Bist

Central Pulp Paper Research Institute Saharanpur
, UP
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CONTENT

• Pulping and bleaching scenario
• Modern Pulping Technologies
• Modern Bleaching Technologies

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The Need for Modern Developments

• Environment Norms
• Increased environmental concern awareness
• Environmental campaign on industrial usee of
  Chlorine and release of Dioxin in Pulp
  Bleaching.
• Enforcement of stringent environmental
  regulations on discharge of Organochlorine
  compounds which resulted in
• - Wider use of extended delignification
• - Oxygen Delignification
• - Eop, Substitution of Chlorine with Chlorine
  Dioxide
• - Secondary treatment of effluents
• Pulp Quality
• Paper Machine runnability
• Strength requirements of end products
• Market Force
• Customer requirement

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Limitations in Indian mills

• Variation in the capacity
• Variation in raw material
• Investment cost
• Typical investment cost for 100000 TPA pulp mill
• Extended delignification 12 million USD
• Oxygen delignification 10 million USD
• ClO2 generation plant 16 million USD

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Pulping Bleaching Scenario (1970-2006)
Enzyme, ECF/TCF Bleaching
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• Variables associated with the raw materials
• Fiber dimensions
• Chemical Composition
• Density- Bulk density/packing density Physical
  size and shape of log
• Moisture content
• Porosity
• Storage conditions

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Major variables

• Chemical composition and sulphidity
• The amount of chemical added
• Bath ratio
• Time/temperature of digester, H factor
• Chip dimensions
• Chip impregnation
• Pressure

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H-FACTOR The H-factor is a way of expressing
amount of Delignification, which takes place
during a cook. As Per definition the H- factor is
the area under a cooking curve of relative
reaction rates vs. time.
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Developments in Pulping Technologies

• Developments in Batch cooking
• Developments in continuous cooking

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Batch or Conventional Cooking

• Until 1950s only Batch digesters were used to
  produce Kraft Pulp
• In late 70s and early 80s following
  developments took place
• Modified Cooking Chemistry Principles (Alkali
  Profiling and low content of dissolved matter)
• Extended Cooking
• Energy Efficient Liquor Displacement Cooking

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Batch or Conventional Cooking
Principles of Liquor Displacement Cooking /
Extended Delignification

• 1. Level out the alkali concentration- lower at
  beginning, higher at end
• High HS- concentration- specially at the start of
  bulk delignification
• Keep dissolved lignin low- especially at the end
  of cooking
• Low temperature.

What is Liquor Displacement Cooking ? Heat and
residual chemicals remaining in Black liquor at
the end of the cooking are captured for reuse in
subsequent batch cooking.
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Conventional Batch Cooking Modified Batch Cooking
Loss of Cooking selectivity at specific Kappa Number Flexibility (Process Raw Material)
Hot Blow results in strength degradation Lower kappa numbers were possible without loss in quality
The fiber undergo mechanical stress resulting into poor pulp strength Respond to environmental challenges
Terminal Displacement - Digester contents are cooled to stop reaction after desired delignification is reached.
High pulp strength delivery and yield
Digestor discharge by dilution and pumping which is a gentle technique
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Strength Delivery of Pulp from Conventional
Displacement Batch Digestors
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Yield vs Kappa Number for Conventional Liquor
Displacement Batch Cooking of Soft wood Kraft
Pulps
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Cooking Cycle (Sunds Defibrator)
Conventional Cooking
Chip Fill 20 Chip Steaming 20 Liq Fill 15 Heating 90 Cooking 60 Degassing Blow 25
Displacement Batch Cooking
Chip Fill 30 Warm Liquor Fill 30 Hot Liquor Fill 35 Heating 20 Cooking 45 Displacement 40 Discharge 30
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Developments in Batch cooking

• RDH
• Super batch
• Enerbatch
• Cold Blow

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Development in Modified Batch Cooking
Rapid Displacement Heating (RDH) Impregnation Temperature is 125-130oC Addition of white Liquor in Impregnation is necessary Upward Flow Displacement
Super Batch Initial Impregnation with Black Liquor at approximate 80-90o C Upward Flow Displacement
EnerBatch Downward Flow Displacement
Clod Blow No warm Impregnation Stage
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• Developments in Continuous Cooking
• First Prototype Continuous Digestor started in
  1938 at a mill in Sweden with capacity of 20 t/d
• First commercial digestor with capacity 30 tons
  per day commissioned in 1948 in a Swedish mill.
• In 1962 in digestor washing called high heat
  washing became available
• High heat washing simplified the brown stock
  washing plant
• 1983 the first mill trials with modified Kraft
  cooking (MCC) were performed in Finnish mill.
• MCC was developed by STFI Royal Institute of
  Technology Stockholm Sweden.
• 65 of global Kraft pulp production is
  manufactured by continuous cooking.

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Developments in Continuous cooking

• Modified Continuous
• Iso Thermal Cooking
• Black liquor impregnation
• Low Solid Cooking

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Development in Continuous Cooking
MCC Split or multiple WL additions for alkali profiling and counter cooking methods to minimize lignin concentration at the end of cook.
EMC High heat wash zone is simultaneously used for cooking and washing.
ITC Advantages High heat wash zone is simultaneously used for cooking and washing Low knots rejects Uniform cook with high yield Improved Bleachability Higher brightness ceiling
Low Solids Pulping Dissolved wood solids are removed from the system by extracting spent liquor at multiple locations First commercial installation in 1993.
Black Liquor Impregnation Advantages Black liquor pretreatment enhances the delignification during Kraft cooking and improves the selectivity of the cook Extracted Black liquor is added to the impregnation vessel with a retention time of 45 minutes. Improved pulp properties , improved tear strength(10 Approx) at the same tensile strength
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Continuous Digester for Agro based Mills (Pandya
Type)
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Cleaner Technology-Pulping
Technology Advantages
RDH, Super batch, Enerbatch CC MCCITC Reduced energy requirement, high pulp yield, Better strength uniformity,Lower kappa, Lower bleaching chemical requirement.
1995- onward
CCMCCITC BLIMCCITC Low Solid Cooking Better Pulp properties Low temperature uniform cooking, better yield
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• Adv/Disadvantages of Conventional Batch Digesting
• Advantage
• Operational flexibility
• Produce diff. Grades in same digester
• Sharp kappa number change
• Tolerant to pins and fines
• Capacity increased by adding digesters
• Less sensitive to chips quality
• Disadvantage
• High energy use
• Limited capability to extended
• Delignification

• Adv/ Disadvantages of Con. Digesting
• Advantage
• More constant steam demand
• More compact less space requ.
• Uniformity in pulp quality
• Extended Delignification possibility
• Better pulp strength
• Disadvantages
• High capital investment
• Restriction for type and raw material quality

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Pulping of casuarina- bole and branch (debarked)
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Modern Development in Bleaching Technology  
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Chemicals Used in Bleaching Processes
Symbol Chemical Symbol Chemical
C Chlorine Z Ozone
D Chlorine dioxide E Sodium Hydroxide
H Hypochlorite X Enzymes
O Oxygen Q Chelating agents (reduce the metal ion Conc.Mn.,Fe,Cu) EDTA,DTPA
P Hydrogen peroxide A Acid
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Functions Economics and Technological
Implications of Bleaching Agents
Oxidant Symbol Code/form Function Advantages Disadvantages
C Cl2 gas Oxidize chlorinate Lignin Effective, Economical Can cause loss of pulp strength
O O2 Gas used with NaoH sol. Oxidize solubilize lignin Low chemical cost,provide chloride free effluent for recovery Large amount required,expensive equipment , lossof pulp strength
H Ca(OCl)2 or NaOCl Oxidize, brighten solubilize lignin Easy to make and use Can cause loss of pulp strength
D Clo2 Oxidize, brighten solubilize lignin Achieve high brightnesswithout pulp degradation,good particle bleaching Expensive, must be made on site
P Na2O2(2-5)Sol. Oxidize, brighten lignin Easy to use , high yield low cost Expensive , poor particle bleaching
Z O3 gas Oxidize, brighten solubilize lignin Effective, Provide chlorine free effluent for recovery Expensive , poor particle bleaching
E NaoH(5-10)Sol. Hydrolyze solubilize lignin Effective economical Darkens pulp
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Reactions and oxidizing equivalents of bleaching
agents
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Selection of right sequence

• Cost of the bleaching chemical
• Selectivity
• Ex. Chlorine being less expensive less
  selective than Chlorine Dioxide was used in the
  first stage CED instead of DEC
• In the end of the sequence its use may
  cause degradation of carbohydrates due to low
  amount of lignin

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Established Pulp Bleaching Sequences showing the
Predominant Role of Chlorine Chlorine Dioxide
in the Industry
Pulp type Sequence
Sulphite Bisulphite pulp
Three stages C-E-H
Four stages C-E-H-H C-E-H-D C-E-D-H C-C-E-H C-H-E-H H-C-E-H C-E-D-D/H E-C-H-D
Five stages C-E-H-D-H C-C-E-H-H
Kraft Pulp
Three stage ,semi-bleached C-E-H D/C-O-D
Four Stage , Partly semi-bleached C-E-H-D C-E-H-P C-E-H-H C-H-E-H C-D-E-D O-C-E-H O-C-E-D O-D-E-D O-D-O-D
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Established Pulp Bleaching Sequences showing the
Predominant Role of Chlorine Chlorine Dioxide
in the Industry
Pulp type Sequence
Sulphite Bisulphite pulp
Five stages C-E-H-P-D C-E-H-D-P C-E-H-E-H C-E-D-E-D C-E-D-P-D C-E-H-E-D C-H-D-E-D- D-E-D-E-D C-C/H-E-H-H
Six stages C-H-E-D-E-D C-E-H-D-E-D C-E-H-E-H-D C-E-H-D-P-D C-E-H-E-P-D CD-E-H-D-E-D O-C-E-D-E-D O-CD-E-D-E-D O-D-E-D-E-D O-C-D-E-H-D
Seven Stages C-H-H-D-D-D-P
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Modern Development in Bleaching Technology
Lignin removal before chlorination

• OXYGEN PRETREATMENT
• ENZYME PRETREATMENT
• OZONE BLEACHING
• ECF / TCF BLEACHING

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Technology Advantages
Oxygen treatment- Two stage Oxygen treatment High kappa reduction (55) High brightness gain Lower yield loss More selective delignification
Ozone Treatment-TCF Bleaching Better effluent quality
Hot Chlorine Dioxide stage Acid pre treatment Saving of Chlorine dioxide Better brightness development Improves brightness stability/reduced reduction.
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Worldwide production capacity of
Oxygen-Delignified Pulp
Capacity, 1000 AD tons/day
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Evolution of Oxygen-delignification Technology
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OXYGEN DELIGNIFICATION
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Conditions for the Oxygen Bleaching
Pulp Consistency 3-30
Sodium Hydroxide 2 , 1.2
Oxygen Pressure 5 Kg/cm2
Treatment Temperature 120oC
Treatment Time 30 min
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Oxygen Treatment of Wheat Straw Soda Pulp
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Oxygen Treatment of Mix Hard Wood Pulp
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CEH Bleaching of Untreated Oxygen Treated Pulp of
Bagasse
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Single Stage Oxygen treatment
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Two Stage Oxygen treatment
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Typical Process Conditions for Two Stage ODL
Parameters First Stage
Second Stage Temp.
80-85
90-106 Pressure (top) ,bar
7-10
3-5 Retention time,min 20-40
60-80 Kappa Reduction
High
Low Viscosity
modest modest
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Eo-Stage Oxygen Treatment
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PROCESS VARIABLES IN OXYGEN DELIGNIFICATION
Effect of NaOH Addition
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PROCESS VARIABLES IN OXYGEN DELIGNIFICATION
Effect of Temperature
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PROCESS VARIABLES IN OXYGEN DELIGNIFICATION
Effect of Oxygen Pressure
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PROCESS VARIABLES IN OXYGEN DELIGNIFICATION
Effect of Oxygen on final pulp brightness
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Characteristics of CEH OCEH Bleach Effluent
(Untreated) of Bagasse
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Characteristics of CEH OCEH Bleach Effluent
(Untreated) of Bamboo
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• OZONE BLEACHING
•  

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OZONE DELIGLIFICATION

• Ozone has property of de-lignifying the
  cellulose, was discovered 150 Years back by
  Chinese and Japanies, but commercialized in 1960s
  and 1970s.
• About 25 mills are using it for bleaching of
  chemical pulp
• It is a very powerful oxidizing agent
• Very poorly soluble in water, 1g/l
• When generated from oxygen, only 8-12 converts
  into ozone
• It is less selective toward lignin than chlorine
  or chlorine dioxide
• It is a strong electrophile which reacts with
  functional group in residual lignin.
• Most phenolic group in lignin is oxidized by
  ozone.
• More selective towards lignin but its
  intermediate inorganic byproducts formed by
  direct decomposition as HO and Hoo are very
  reactive with carbohydrates.

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Process conditions

• Consistency-
• The consistency is maintained to enhance the mass
  transfer rate between gas and liquid phase, eith
  high or medium consistency is maintained during
  the reaction
• pH-
• Ozone delignification is more efficient at pH
  value near 2. The low kappa and better viscosity
  is achieved at pH 2 than pH 4 or 6.
• Temperature
• The best selective temperature range is 25-30oC.
• Time - 2-5 Minutes
• Additives- several additives as formic acid,
  acetic acid, methanol etc. are reported, for
  preservation of carbohydrates combination of
  dioxide with ozone is also a good substitute..

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• OZONE AS REPLACEMENT OF CHLORINE-
• The ozone can be a substitute of chlorine, but
  this fact is not realistic in case the initial
  kappa number is high. It requires low kappa
  number entering to bleach plant (lt10)
• Most commercial installation are after oxygen
  delignification in DZ or ZD combinations
• Placing the Z stage towards the end of the
  sequences found to increase the brightness and
  reduce the Ozone requirement
• Placing Z stage between two peroxide stages
  reactivates the pulps and it responsd better to
  the second peroxide stage.

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LABORATORY BLEACHING RESULT FOR A OXYGEN
DELIGNIFIED KRAFT PULP OF KAPPA 15(OZONE
0.5,CY 10, EDTA AT PH 6.3 AND H2O2 2.5 AT PH
11)
Sequence Kappa number after bleaching Brightness,ISO
Z 9.9 46.7
QP 7.1 71.1
QPP 5.9 77.9
ZQP 3.6 77.5
QPZ 2.7 77.6
ZQPP 2.8 83.9
QPZP ND 89.9
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ECF / TCF BLEACHING
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ECF/TCF Bleaching
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DIFFERENT ECF/TCF BLEACHING SEQUENCESS
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Bleaching Sequences Designed to reduce or
Eliminate the use of Chlorine Based Compounds and
Chlorine
Application Bleach sequence
Reduced chlorine (C)-P-H (C)-P-D-H (C)-P-H-D-H
Peroxide replacement P-D-P P-D-H P-H-H P-H-D D-P-D P-H-D-H P-DP-D
Oxygen bleaching O-P O-D O-H O-P-D O-D-P O-C-P O-H-P O-C-P-D O-D-P-D
Ozone bleaching Z-E-P Z-E-Z Z-E-Z-P
Peracaetic acid P-A-P A-E-A-E-A
others O-Q-P O-Q-P-P O-Q-P-Z-P